The present invention relates to a joiner for lance joining ductile materials, such as metal sheets, and in particular to a joiner including a die assembly and a punch assembly.
It is known to join a plurality of sheets of ductile material by causing these to be deformed into an interlocking configuration in a local area. Such joins are made by ductile material joining tools comprising a die with an aperture that is opposite a punch assembly comprising a punch surrounded by a stripper mechanism. Layers of ductile material are sandwiched between the punch assembly and when the punch is pressed towards the aperture, material is drawn into the aperture. The material undergoes plastic deformation in the aperture to flow into a shape in which two or more layers are interlocked, for example by the forming of one layer around another layer.
The aperture has a base with an anvil having an anvil surface and at least two side walls formed from movable blades. The blades are generally transverse to the anvil surface and extend in the direction in which the die and punch are pressed together. The blades help define the local area, for example a circular, square or rectangular area, in which the deformation of the layers of sheet material takes place. Once the material has been drawn and flows into the aperture, the blades move away from each other in a radial direction as sheet material flows laterally. Some types of die blade pivot outwards about a pivot mechanism below the level of the anvil surface. The pivot mechanism has a pivot axis or pivot point below and laterally outside an edge of the anvil surface.
The outward movement of the blades is constrained by a die shield, which extends around the die held in a fixed relationship with the die. In many designs, the space taken up by the pivot mechanism and die shield tends to increase the size of the die, which is inconvenient when a die must be small, for example when used in confined circumstances such as making joins near corners of sheet metal.
A circular die and punch can be used to form a clinch joint in which sheet material is symmetrically deformed both axially and radially to form a leak-proof button, for example as disclosed in patent document U.S. Pat. No. 5,153,513. A square or rectangular die and punch can be used to form a trapezoidal clinch joint (also called a lance joint), in which the sheet material is cut through by the punch along a pair of parallel opposed lines, with the layers of sheet material deformed laterally outwards underneath each of the cuts, as disclosed in patent document GB 2,334,474. The present invention relates to a die and punch for forming a lance joint, and the terms xe2x80x9clance joinerxe2x80x9d and xe2x80x9clance jointxe2x80x9d will be used respectively for such clinching devices and clinch joints.
It is known in the prior art to include in the die some biasing means of biasing the die blade back towards the anvil surface after the drawing operation by the punch is completed. For this, a coil spring, leaf spring, or elastomeric o-ring can be provided., which may extend fully around the outside of the die blades. As the die blades move outwards to dilate the aperture, the spring or o-ring becomes stretched or compressed. When the joined sheet material is withdrawn from the aperture, the die blades return to their start position owing to the tension or compression in the spring or o-ring.
Because the spring or o-ring extends around the outside of the die blades, usually between the die blades and the surrounding die shield, lateral space must be provided for the spring or o-ring. Lateral clearance space can result in a die blade being dislodged from between the anvil and die shield, and being lost from the die, particularly if a spring or o-ring breaks. This is very inconvenient in a production environment, as any machine using the sheet metal joiner would then have to be stopped to repair or replace the faulty die. If the faulty die were not spotted immediately, a great deal of rework to joined fabrications might then be required.
The lifetime of a die is limited essentially by the die blades. The upper inward corner of the die blade must form a sharp edge of about 90xc2x0, but this will become dull with excessive use. When clinch joining hard metals, such as stainless steel, the lifetime of a die blade may be as short as 10,000 to 20,000 cycles. In order to maintain join quality, it is necessary to keep to a conservative schedule for changing die blades, which adds to manufacturing cost.
A rectangular or square die for lance joints inevitably has four corners around which a spring or o-ring must pass. These corners, even is somewhat rounded, are a source of wear on the biasing means. It can be very difficult to predict when a spring or o-ring may break, or need changing. A spring or o-ring may also become damaged by the corners when die blades are changed, and this makes failure of the biasing means more unpredictable.
A breakage of a spring or a die blade may not be noticed immediately in a production environment, and will result in faulty joins and/or damage to the work pieces being joined.
It is an object of the present invention to provide a die, for a ductile material lance joiner, and also a ductile material lance joiner for lance joining two or more layers of ductile material, which addresses these issues.
Accordingly, the invention provides a die for a ductile sheet material lance joiner, comprising:
a) a die anvil, the anvil having an anvil surface;
b) at least two die blades around the anvil, the blades extending in a longitudinal direction, generally above and below opposite sides of the anvil surface and forming with the anvil surface a die aperture for a die punch, each die blade being arranged to move away from the anvil to open up the die aperture when ductile material is forced in the longitudinal direction into the die aperture and against the anvil by a die punch, and each die blade having a cutting edge above the anvil surface and facing towards the die aperture for cutting through ductile material to make a lance joint when said ductile material is forced into the die aperture; and
c) at least one biasing means by which the die blades are biased towards the anvil to constrict the die aperture;
characterised in that each die blade can be removed from the anvil and then returned to the anvil in such a way that each die blade is essentially rotated relative to the anvil surface about the longitudinal direction to present a different cutting edge above the anvil surface and facing towards the die aperture.
Each die blade may therefore be provided with two cutting edges above the anvil, a first one of which at any one time faces in towards the die aperture, and a second one of which faces outwards from the die aperture. The first cutting edge can then be used until it becomes blunt, and the die removed from the anvil and rotated relative to the anvil surface about the longitudinal direction, and then returned to the anvil with the second cutting edge positioned so that this can be used as the cutting edge. This allows the lifetime of each die blade to be effectively doubled.
The die blades may move by sliding or pivoting, for example on a shoulder extending laterally away from and below the anvil surface, in order to open up the die aperture. If the die blade pivots, then the pivot point is preferably below and laterally outside the anvil surface.
In a preferred embodiment of the invention, there is for each die blade a pivot recess in the anvil. Each die blade then has a seat that is shaped to match the pivot recess so that when the die blade is seated in the pivot recess, each die blade can rotate outwards from the anvil to open up the die aperture when ductile material is forced in the longitudinal direction into the die aperture and against the anvil by a die punch. Such a pivot recess helps spread the load on the die blade imparted by the die punch. A rotational pivot also provides a low friction seat, even without lubricant, that essentially does not wear over the lifetime of the die blade.
The anvil may be rectangular or square with a pair of die blades on opposite sides of the anvil, and a pair of opposite parallel sides that extend between the die blades. The biasing means can then extend around the die blades and this pair of opposite parallel sides. An advantage of this arrangement, when the die blades may be removed form the anvil along a transverse direction to the longitudinal direction, is that the biasing means helps to retain the die blades to the anvil.
Also according to the invention there is provided a die tool for lance joining two or more layers of ductile material, comprising a base plate, a recess in the base plate, and a die, the die being seated in the recess, wherein the die is according to the invention, and the recess serves as a die blade shield to limit the movement of the die blades away from the anvil.
The invention also provides a ductile material joiner for lance joining two or more layers of ductile material, comprising a punch and a die with a die aperture matching the punch, wherein the die is according to the invention.
The invention further provides a method of servicing a die for a ductile material lance joiner, the die being according to the invention, wherein the method comprises the steps of:
i) removing one or more of the die blades from the anvil;
ii) returning the die blade to the anvil in such a way that each removed die blade is essentially rotated relative to the anvil surface about the longitudinal direction to present a different cutting edge above the anvil surface and facing towards the die aperture.
One way of accomplishing the relative rotation of the die blade relative to the anvil surface is by removing the die blade from the anvil, rotating the die 180xc2x0 about an axis passing through the die blade in a direction parallel to the longitudinal direction, and then returning the die blade to the anvil.
An alternative way of accomplishing the relative rotation of the die blade relative to the anvil surface is by removing a pair of opposite die blades from the anvil, and then without altering the orientation of the die blade relative to an axis passing through the die blade in a direction parallel to the longitudinal direction, returning each die blade to the anvil in the location originally occupied by the other die blade.